Nature's Law
by BrandNewDay
Summary: Cake, jealousy, a party...what else could possibly happen in their latest case? A Cal/Gillian fic.
1. Chapter 1

**Disclaimer: I do not own the show Lie to Me or it's characters. I'm guessing you probably knew that, but, just in case you didn't. (:**

* * *

"We have a case that we'd like you to look into," Agent Mitchell, the FBI agent seated across from Cal Lightman and Gillian Foster, stated. Cal shifted in his chair impatiently; he wanted Agent Mitchell to get to the point already. They already had a few other tedious cases to finish, and Cal wanted to get them over with before it was time to leave. "A millionaire was murdered and one of the suspects is hosting a party tomorrow night. You know, not a wild party, but a more formal one. The person holding the party, Roy Jenson, supposedly had something against Mike Jacobs, the murdered millionaire, but we don't have enough evidence to bring him into custody. He's been very uncooperative with us, and we'd like you to go to the party to find out more about his conflict with Jacobs and any information about the murder. Just don't let him know you're investigating him. Like I said, he's not very friendly with anybody involved in solving this case."

"So you basically want us to go undercover at his party to see if he had anything to do with the Jacobs murder?" Gillian asked. Cal shifted his gaze to Gillian. For a moment, he forgot about the case completely, his mind drifting to her and her recent divorce. How they still had that damn line, how he really wanted to cross it, how he-

Cal quickly shook those distracting thoughts from his head and returned his attention back to the FBI agent sitting across from him.

"Yeah, it would be a great opportunity to find out more about the guy," Agent Mitchell claimed. The FBI agent displayed no signs of impatience, leading Cal to believe he definitely had a better temper than Agent Reynolds, their usual FBI guy. "We don't have much information about him; he's a more keep-to-himself type of person. As for the party, you could bring a date if you wanted; the invitation mentions that you're allowed to bring a guest." Agent Mitchell gestured to the folder in front of him, most likely holding the invitations, and paused for a moment. "And we'd recommend trying to act like a typical guest by grabbing a few refreshments, mingling with the guests, which would help with the investigation, and even dancing to a few songs would be great. Anything to prevent you from looking suspicious." Cal knew Gillian didn't have anyone to invite, and he himself didn't either, but if they were expected to _dance_…

"…so Roy Jenson also has a son, Blake Jenson, that you might want to keep an eye on," Agent Mitchell continued. "Blake is supposedly getting ready to take over Roy's business soon, and Roy could've involved him. You might want to look out for the guests, too. Roy could've had anyone do the dirty work for him." Agent Mitchell stopped for a moment before continuing again. "Will you take the case?"

Cal exchanged a look with Gillian, and instantly knew she was okay with it. They could easily tell what the other was thinking without any words. They knew each other pretty well, and the fact that they specialized in microexpressions helped a bit, too. "We'll go," Cal stated simply to the FBI agent.

"Great," Agent Mitchell responded as he picked up the manila folder lying on the table in front of him. "This folder contains everything you'll need to know and the invitations you'll need to get in. Remember, try to blend in with the other guests, but while doing that, talk a little bit to Roy Jenson and his son as well. More importantly, don't let them find out what you're up to." Agent Mitchell got up to leave. "I'll probably contact you later, when the time of the party is closer."

* * *

Cal sat in his office, waiting for Gillian. They had decided to meet in his office when they were ready to leave. He himself forced to wear a tux, as the party _was _formal. Agent Mitchell had visited the office earlier with a few last minute answers and adjustments about their plan, like how they were to arrive at the party in a limo. Cal wasn't so sure if he wanted to go undercover; Agent Mitchell's suggestions didn't help much, yet the fact that he was supposed to 'pretend' Gillian was his date seemed to lift his spirits.

Cal checked his watch to find that it was already time to leave. '_Where is Gillian?' _he thought.

As soon as he looked away from his watch, he saw Gillian entering his office. Suddenly, all Cal's doubts about this case disappeared. Gillian was wearing a black dress that fit in all the right places, leaving Cal speechless.

"Hey," she said, coming to a stop in front of his desk. "Sorry I'm late." It seemed like forever to the two before Cal snapped out of his wordless state.

"Hey, uh," Cal stuttered, still recovering a little. "You look…you look fantastic." Gillian blushed as she realized Cal was at a loss for words.

"You look nice, too," she managed to reply, and she meant it. The room was silent for a moment as they gazed at each other longingly. A sudden knock on the door made them both turn to the door.

"Loker and I just got back from a case," Torres stated, looking curiously from Cal to Gillian. She could tell something was going on between the two. "The driver of the limo parked outside asked me to tell you to get out there."

"Okay," Gillian said, glancing back at Cal. "Ready?"

"Yeah." Cal stood up and the two walked quietly outside to the limo waiting outside in the parking lot. The driver was pacing outside of the limo and staring at the ground. Cal and Gillian exchanged an amused look as the driver constantly checked his watch.

"Finally, you're here," the driver mumbled, more to himself than to Cal and Gillian. "We have to leave now or else we'll be late." The driver raised his voice to an audible level on his last comment.

"I'm sure we'll get there on time," Gillian confirmed as Cal grudgingly noticed the driver's eyes dilate as he turned his attention to Gillian. Sexual arousal.

"Yeah, yeah. Agent Mitchell _did _send a tight schedule, you know…" The driver seemed to be lightening up after Gillian's response, and Cal didn't like that at all. "I'm Eric Granville, by the way. I'll be taking you to the party." Cal impatiently walked over to the limo and opened the door.

"We better get going then," Cal interrupted, allowing Gillian to enter the car first. She smiled in thanks, and Cal returned the smile. Before getting in the car himself, he glanced back at Granville and was glad to see the annoyed look on the driver's face. Cal got into the limo, just as Granville slid into his seat in the front of the car.

"Got your invitations?" he asked grumpily. Cal reached into his pocket and felt the smooth paper underneath his hands.

"Yeah," Cal replied casually.

"Good," Granville said gruffly as the limo pulled out from the parking lot.

* * *

"Here it is," Granville announced as they came in view of the mansion the party was being held at. The limo pulled into the long driveway, holding a few other limos and fancy cars, and came to a stop. "Should be someone at the entrance that'll let you in once you show 'em your invitation."

"Okay, thanks," Cal said quickly before bolting out the door. To his dismay, Granville was already there to open the door to Gillian.

"Thanks," Cal heard her say. He quickly turned to the mansion in thought. The driver was just being friendly that's all, right? Nothing to be jealous about. Why was he jealous, anyway? Before he knew it, Gillian was right there beside him.

"Let's go," she said, catching a glimpse of the look on Cal's face. Soon Cal noticed the amused smile she wore that followed right after.

"What?" he asked, although he could guess what the answer would be.

"You weren't so friendly to our driver," Gillian responded still smiling.

"You never can trust those limo drivers, you know," Cal teased innocently as they finally arrived at the entrance to the mansion.

"Invites?" the guy standing guard asked. Cal rummaged through his pocket and quickly found the invitation.

"She's with me," Cal said as he gave the guard his invite. He let Cal and Gillian into the room with an expressionless nod.

"See the Jenson's?" Gillian asked Cal quietly as she glanced around the room.

"Not yet," Cal said, remembering what they were there for and started searching the room as well. He couldn't find anyone in the room that resembled the pictures Agent Mitchell had showed them earlier.

"Oh, look, there's cake!" Gillian exclaimed excitedly, pointing across the room to a table filled with food and refreshments.

"You really love that type of stuff, don't you?" Cal asked, wondering how she could actually like sugary food like that.

"Hey, welcome to the party," someone said before Gillian could respond to Cal's remark. They both whirled around to see a man that matched the image of Roy Jenson's son, Blake.

"I'm Blake Jenson, by the way," he continued with his charming smile. "My father's the host of the party, so I'm here to help moderate." Cal observed the disgust that flickered across Blake's face as he mentioned his father when something else captured his attention. He noticed the same dilation of the eyes that their limo driver had shown when he saw Gillian.

_Great. _Cal thought sarcastically. _Another guy who's aroused by Foster. Just what we need._

_

* * *

_

**Author's Note: This was originally going to be a oneshot(where a few parts of the next chapter would be combined in this one), but after reading over this chapter, I have a few more ideas about what else could happen. I didn't feel like writing a oneshot _that_ long, so it'll be a multi-chaptered story instead. Hope you like it. xD**


	2. Chapter 2

"I'm Gillian Foster," Gillian said, turning to Cal to introduce himself.

"Cal Lightman," he said, not liking the look Blake was giving Gillian. It was as if he was going to ask her to dance or something…

"Hey, aren't you the people who detect lies?" Blake questioned, suddenly turning suspicious. Agent Mitchell had told them that they didn't need to use false names; he said that it wouldn't matter if the Jenson's knew what they did for a living, as long as they didn't know what they were there to do. Cal personally didn't believe that, but decided to just go along the the FBI agent's plan.

"Yeah, that's us," Cal responded, seeing the distrust flash across Blake's face. Cal noticed as Blake's face grew serious.

"You're not here to interrogate my father about the murder, are you?" he asked, lowering his voice so the guests around them couldn't hear.

"What murder?" Cal asked, pretending to be clueless. His acting seemed to be working on Blake.

"The-" Blake stopped his sentence and smiled. "You probably never heard of it. Sorry, my father's been getting annoyed at how much questions he's getting for the case…" Cal watched as Blake turned his gaze back to Gillian.

A new song was now playing in the room, and Cal took this as his opportunity to get away from Blake.

"Well, we were just going to dance," Cal said, gesturing to the other side of the room. "Nice meeting you." Cal quickly led Gillian to the dance floor before Blake could say anything else.

"That was close," Gillian told Cal quietly.

"Yeah," Cal replied, before realizing that Gillian was probably talking about their undercover status, not the way Blake was looking at Gillian…

"He's still watching us." Gillian observed, taking a quick glance behind them.

"We should probably dance then, shouldn't we?"

Gillian nodded, as Cal put one hand on her shoulder and one around her waist. She did the same, and soon they were dancing together. The two listened to the song that was now beginning to play without recognizing it.

_I tried to fight the feeling, the feeling took me down,_

_I struggled and I lost the day you knocked me out,  
Now everything's got meaning and meanings bring me down,  
I'm watching as a screening of my life plays out._

Cal felt like the song described him: he always had to 'fight' his feelings for Gillian, whether he wanted to or not. They had the line, the line they couldn't cross no matter how much he wanted to. There were all these other reasons, like how he was married to Zoe and how Gillian was married to Alec…but that reason didn't apply anymore.

_Every day I fight these feelings,  
For your sake I will hide the real thing,  
You can run all your life, all mine I will chase..._

_You should never fight your feelings  
When your very bones believe them  
You should never fight your feelings  
You have to follow natures law._

They were gazing into each other's eyes now, as if the song was notifyinging them about their relationship: how they were now, how he wanted it to be, how it could be…

_I'll live with never knowing, if knowing's gonna change,  
I'll stop the feeling growing, I will stay away,  
Like a broken record stuck before a song,  
A million beginnings, none of them the one.  
Every day I fight these feelings,  
For your sake I will hide the real thing,  
You can run all your life, all mine I will chase..._

The song was slowly starting to fade away; Cal's focus was soon entirely on Gillian, who seemed to have the same feelings…

A few more seconds pass before Gillian broke the eye contact and glances at the ground. After reading the thoughtful expression on her face, Cal did the same.

_You should never fight your feelings,  
You have to follow nature's law._

With the song ended, Cal and Gillian made their way over to the side of the room.

"There's Roy Jenson, over there," Gillian told Cal, casually nodding to the right although Cal could tell that she was thinking about something else. Cal glimpsed over at the direction, and saw the older version of Blake Jenson talking to the man beside him.

_And there's Blake, _Cal thought, deciding it was better if Gillian didn't know. He wanted to avoid Blake in whatever way he could, and he didn't know if she would feel the same way. "Let's…grab some cake," Cal suggested, grabbing Gillian's arm and leading her over to the other side of the room. He saw Blake was making his way towards them giving Gillian the same aroused look as before.

"Are you feeling okay?" Gillian joked with an amused smile as Cal took another look at the table. "You seriously want some cake?"

"Yeah, why not?" Cal remarked, glancing back at Blake. He seemed in a disappointed mood, which lightened Cal's. He picked up a plate of cake and handed it to a still-confused Gillian. Hesitantly, he grabbed one for himself.

"Wasn't that Blake Jenson who was walking towards us?" Gillian asked, the amused look back on her face.

"Oh, really? Didn't see him," Cal lied unconvincingly. Gillian shook her head as she smiled to herself. She had a feeling that there was a reason Cal would be running away from one of their suspects.

"You sure this stuff is safe to eat?" Cal questioned, poking at the cake with his fork. "Looks like it's too sugary for me." He jokingly started to move it towards the garbage.

"Hey," Gillian said, guiding Cal away from the garbage. "You said you'd try it."

* * *

Seeing the two laughing and smiling each other, Blake decided to look for someone else. He probably didn't even have a chance with her, not with the way the two looked at each other. He saw how they danced, as if they were suddenly oblivious to everyone else in the room. Even now, as they were playfully messing around with their cake, he could tell they shared a bond that he wouldn't be able to break.

* * *

"This actually isn't that bad," Cal said, cautiously chewing the small piece of cake that Gillian had finally persuaded him to eat.

"I told you," Gillian said as she took another bite from her own cake. _For an undercover mission, this is actually fun_, Cal thought, realizing the one person he wanted to be with was right in front of him.

* * *

"So, were you able to read anything off of him?" Agent Mitchell asked as soon as the two returned back to their office.

"Yeah," Cal asked, entering the room in a lighter mood than he had been in a while. "Roy Jenson didn't have anything to do with the murder. You might want to ask his son, Blake, though."

"When we talked to Blake, he showed a little guilt for his father," Gillian explained, seeing Mitchell's clueless expression to Cal's suggestion. "He also didn't like how everyone was bothering his father about the murder, and that could mean that he doesn't want his father to have to pay for something he didn't do."

"Blake murdered Granville?" Mitchell questioned, confused.

"Yeah, and if you want all the details, I'd ask him yourself," Cal replied before impatiently leaving the room.

"I'll give you the payment as soon as possible," Mitchell told Gillian, who smiled as she slightly shook her head at Cal's quick exit. "And, uh, I was wondering…"

Cal, who still could hear the conversation, stopped in his tracks. Mitchell's vocal pitch had left its 'strictly-work' mode, and Cal didn't like the pitch that it had changed to.

"Oi, Foster!" Cal said as he walked back into the room before Mitchell could finish. Seeing the two shift their attention on him, he continued; "Got a new case. Better get started." Cal turned back to Agent Mitchell. "Nice working with you, by the way." He led Gillian out of the room, leaving Mitchell in the office, flustered.

"And what's so important about this case?" Gillian asked, glancing behind her to see Mitchell slowly making his way to leave the office.

"There isn't one," Cal replied, finally coming to a stop inside Gillian's office and taking a seat on the couch.

"Then why…?" Gillian stopped as she took a seat beside Cal on the couch. "You thought he was going to ask me on a date, didn't you?"

"Was he?" Cal asked. Taking his answer as a yes, Gillian smiled. That was as much of a confirmation that she needed; Cal had been trying to prevent everyone-Blake Jenson, Eric Granville, and Mitchell- from flirting with her.

"And Blake Jenson, the cab driver…?" Gillian asked, amused. Cal was _jealous_.

"Didn't think you'd want to date a murderer or a driver." Cal replied jokingly. "Thought you went for more of the lie detector type."

Before Gillian could respond, Heidi walked into the room. "Emily's on the phone; she wants to talk to you." Heidi left, and Lightman turned to leave as well.

"Dinner tonight?" he asked Gillian before exiting the room.

"Sure." Gillian replied with a smile.

"See you tonight then, love."

* * *

**Author's Note: **Sorry for the _really_ long wait! I had two ideas on how I could continue this story, and I finally chose this one. The actual case seemed sort of short and random to me, but I wrote this more for the 'fluff' and jealousy so...I hope you liked this story anyways(and this is the last chapter, in case you're wondering), and thank you so much for all of the reviews!

The lyrics used are from the song 'Nature's Law' by Embrace. (:


End file.
